A crustal transect between Precambrian Australia and the Timor Trough across the Vulcan Sub-basin

• Published in: Tectonophysics 2000-12, Vol.329 (1), p.23-38
• Main Authors: Petkovic, P., Collins, C.D.N., Finlayson, D.M.
• Format: Article
• Language: English
• Subjects: lithospheric velocity structure; Marine; Moho; Northwest Australia; Ray tracing; seismic refraction; Vulcan Sub-basin
• ISSN: 0040-1951; 1879-3266
• DOI: 10.1016/S0040-1951(00)00186-4

Wide-angle seismic data from ocean bottom seismographs, together with gravity and deep marine reflection profiling data along the Vulcan transect in northern Australia, define the crustal-scale features between the Precambrian Australian craton and the Timor Trough. The transect provides an outline of crustal and upper mantle architecture across the major boundary between the Australian and SE Asian plates when linked with earlier deep marine seismic profiling. Near the Australian coast, relatively unaltered Precambrian Kimberley Basin rocks are inferred to extend to the edge of a shallow-water shelf area (Yampi Shelf) with a crustal thickness of 35 km. The crust then thins to 26 km under the outer shelf near the Timor Trough. Over the same distance Palaeozoic/Mesozoic basin sequences are interpreted to thicken to 12–13 km, inferring an attenuation of Precambrian basement rocks from 35 to 13–14 km across the margin ( β=2.6). On the outer shelf, the Vulcan Sub-Basin is a trans-tensional rift within Permo-Triassic platform areas (Ashmore Platform, Londonderry High). Within the lower crust under major bounding faults at the sub-basin/platform margins, there are elevated P-wave velocities to 7 km/s, suggesting emplacement of intrusive, more mafic rocks at depth during basin-forming processes. At mid-crustal levels, near the top of the inferred attenuated Precambrian crustal rocks, there are strong near-vertical-incidence reflections at about 13 km depth that are interpreted to be a detachment or further evidence of intrusive rocks. Additionally, seismic energy reflected at wide angles from within the upper mantle at 38–45 km depth indicates that compositional boundaries/heterogeneities continue at depth. Detailed information within the basin sediments includes the interpretation of crosscutting velocity patterns within the Mesozoic sequences as an indication of decreasing porosity with depth of burial, and the presence of a low-velocity sequence at 1–2 km depth across the Londonderry High.